A new mass-spectrometric technique relies on ionization during bombardment of the analyte (dissolved in a liquid matrix, usually glycerol) by an atom beam (e.g., Ar0, Xe0). This technique, termed "fast atom bombardment," is particularly useful in the characterization of polar charged molecules. A neutral beam is not essential, and a primary beam of cesium ions has been successfully used to produce spectra equivalent to those obtained by fast atom bombardment. In this communication I report data on the use of both ion and atom primary beams for producing secondary-ion mass spectra of conjugated steroids. In negative-ion spectra produced for steroid glucuronides and sulfates, the ion [M - H]- is invariably the major high-mass peak, and the lack of substantial fragmentation allows assay of relatively complex mixtures if the analytes differ in mass. I describe here the use of secondary-ion mass spectrometry for distinguishing, by urinary steroid analysis, patients with the four enzyme defects that can affect cortisol synthesis: defects in 17 alpha-hydroxylase, 3 beta-hydroxysteroid dehydrogenase/isomerase, 21-hydroxylase, and 11 beta-hydroxylase.